The present invention relates to a furnace grate structure over which solid fuel advances in a direction of conveyance as the fuel is combusted, and more particularly to a furnace grate structure having a plurality of grate beams extending substantially parallel to one another and substantially transversely to the direction of conveyance, with the grate beams being supported on a substructure.
At least one bank of elongated grate bars of the furnace grate structure extend substantially parallel to the direction of conveyance in spaced relation to each other. Upwardly facing support surfaces of the grate bars are inclined downwardly in said direction of conveyance for conveying the solid fuel. Each of the bars is supported at each end thereof on a mounting surface of a respective grate beam, such that some of grate bars are reciprocatingly movable in a substantially horizontal direction and the other grate bars are stationary.
By means of the fact that several banks of grate bars can be arranged one behind the other like steps, the grate structure is thereby subdivided. A particularly beneficial and adaptable stirring effect is achieved when some of the grate bars are moved back and forth in a substantially horizontal direction. By regulating the grate movement in the individual banks of grate bars, inclined grate structures of this type can be adapted to the characteristics of various fuels.
Because of the high thermal loads to which such inclined grate structures are subjected, the grate beams serve primarily as a framework to support the grate bars on the substructure which is made of steel and cannot withstand the thermal loads. For this reason, the grate beams generally consist of a grey cast iron that can withstand the thermal loads.
A furnace grate structure of this type is described in U.S. Pat. No. 4,638,905, assigned to the same assignee as the present invention, where at least one of the grate beams comprises a plurality of grate beam sections, which are arranged end to end on said substructure to form a grate beam having gaps between adjacent grate beam sections.
According to the U.S. Pat. No. 4,638,905, keyed engagement means are provided on said grate beam sections for guiding and laterally positioning the reciprocatingly movable and said stationary grate bars such that each of the gaps between the adjacent ends of said grate beam sections are covered by preferably stationary grate bars.
In the preferred embodiment of the afore-mentioned patent, the gaps between the adjacent grate beam sections are covered by stationary grate bars in which each of the shortest grate beam sections supports two stationary grate bars partly for covering the gap between the adjacent grate beam sections and between the stationary grate bars one grate bar being reciprocatingly movable parallel to the direction of conveyance.
In said known inclined grate, the lateral arrangement o the grate bars mounted on the grate beams is fixed because the separating gaps between the adjacent grate beam sections must be covered by the stationarily mounted grate bars.
Furthermore, in the known inclined grate, every grate beam section must be capable of supporting two stationary grate bars partly and between them at least one reciprocating grate bar, thus limiting the shortest length of each grate beam section and the flexibility of the furnace grate structure.
Finally, because of the displaced arrangement of the grate bars on the grate beam sections in the known inclined grate, special and different end sections for abutment against the side walls of the furnace chamber are necessary, so that it is always necessary to provide three different shapes of grate beam sections for a variable-length grate beam.